Vapor jet pump



May 26, 1959 R. A. DENTON VAPOR JET PUMP Filed Nov. 22, 1957 INVENTOR. Richard A.Den=i:on

Afiornegs United States Patent VAPOR JET PUMP Richard A. Denton, Haddonfield, N.J., assignor to The lJWew York Air Brake Company, a corporation of New ersey Application November 22, 1957, Serial No. 698,087

4 Claims. (Cl. 230-101) This invention relates to vacuum pumps and more particularly to vacuum pumps of the vapor jet type. The term vapor jet pump is used herein in its generic sense and includes diffusion or condensation pumps as well as ejector pumps.

One class of pumps of this type in common use today, viz. the diffusion pump, generally includes a cooled cylindrical housing, a coaxial cylindrical jet chimney located within and spaced from the housing, one or more series of circumferential jet openings through the wall of the chimney and a frustro-conical jet skirt associated with each series for directing the vapors issuing from the openings across the annular entraining area between the chimney and the housing. The speed of the pump, i.e., the rate of entrainment of gas molecules in the vapor jet, depends on the size of this annular entraining area. Devices for increasing the size of the entraining area have been proposed, but none of them has been altogether satisfactory. One of the major disadvantages of these prior devices is that they do not afford effective means of condensing the vapor molecules which traverse the entraining area. As a result, some of the vapor molecules will backstream through the pump inlet and into the system being evacuated. In large pumps, this problem is particularly serious because the radial width of the entraining area is large.

The object of this invention is to provide an improved nozzle and condensing surface for vapor jet pumps which afi'ord high pump speed without undue backstreaming of vapor molecules. According to the invention, a separate nozzle and condensing surface are employed for each jet opening. In the preferred form, the nozzles have the form of the projecting portions of a fluted thin-walled truncated cone and they are spaced around the outer periphery of the jet chimney. The condensing surfaces are thin radial bafiies which are attached to and in heat conducting relationship with the cooled housing. The bafiies are spaced around the inner periphery of the housing and project into the spaces between adjacent nozzles to form entraining areas which surround. the nozzles. In this way, the size of the entraining area of the pump can be increased without increasing its width. This results in higher pump speeds and minimum backstreaming.

A preferred embodiment of the invention will now be described in relation to the accompanying drawing, in which:

Fig. l is an axial section of a vacuum diffusion pump employing the improved nozzles and condensing surfaces; the boiler and jet chimney being shown in half-section.

Fig. 2 is a sectional view taken on line 2-2 of Fig. 1.

Fig. 3 is a view taken on line 3-3 of Fig. 1 and shows a modified form of condensing surface.

Fig. 4 is a perspective view of the top portion of one of the baffles of the Fig. 3 embodiment.

Fig. 5 is an elevation view, partly in section, showing an ejector pump employing the invention.

As shown in Fig. 1, the diffusion pump comprises a which is isolated from inletopening 12 by a conical bafiie 21. A cooling coil 22 surrounds that portion of the housing 11 between outlet opening 12 and fore pump connection 13. I

Associated with each jet opening in the three series 16, 17 and 18, is a radially extending expanding nozzle 23 which is formed in the shape of a projecting portion of a fluted thin-walled truncated cone, and is arranged to discharge toward fore pump connection 13. The size of nozzles 23 increases progressively from series 16 to series 18 so that the radial distance 24 between the outer edge of the nozzle and the housing decreases progressively from the inlet 12 to the outlet 13. This is a common practice in the diffusion pump art and affords a workable compromise between pump speed and fore pressure tolerance. Between nozzles 23 are mounted thin radial baffies 25 which extend from inlet 12 to outlet connection 13. The baflles are attached to and in heat conducting relationship with the housing 11.

The opposed surfaces of adjacent, baffies 25, together with that portion 26 of housing 11 located between them, constitute a generally U-shaped vapor condensing surface. This surface and the outer periphery of nozzle 23 defines an intervening entraining area 27 surrounding each nozzle 23.

In operation vapors, either oil or mercury, generated in boiler 14 will be transmitted to the jet openings in the three series 16, 17 and 18 by chimney 15. The jets of vapor issuing from these openings will be directed, by the associated nozzles 23, toward fore pump connection 13. In a well known manner, the vapors crossing entraining areas 27 will entrap gas molecules entering the pump through inlet opening 12. The vapor molecules will condense on the condensing surfaces formed by bafiles 25 and housing portions 26, whereas the gas molecules will proceed through the pump and be withdrawn through fore pump connection 13. Vapor condensate will gravitate toward the bottom of housing 11 and return to boiler 14 via passages 33.

Figs. 3 and 4 illustrate a modified form of the invention in which the thin radial baffles 25 of the preferred embodiment are replaced by prismatic baflies 34; the remaining parts of the pump being the same. The upper ends of these bafiles, i.e., the ends adjacent inlet opening 12, are tapered as shown in Fig. 4, so that gas molecules impinging thereon will be directed into the entraining areas 35 surrounding the nozzles 23. By using the prismatic bafiles 34 and properly shaping their faces 36, it is possible to obtain an entraining area 35 having a substantially uniform width. This embodiment, therefore, afiords more uniform condensation of pumping vapors than the Fig. 1 embodiment.

In Fig. 5, the nozzles and bafiies, of the Fig. 1 embodiment have been incorporated in a conventional ejector pump 37 having an inlet and outlet 38 and 39, respectively, and a cooled Venturi section 41. A jet chimney 42 transmits pumping vapors from a boiler 43 to a circular series of four jet openings 44. Each jet opening is provided with a nozzle 45, having the same shape as the nozzles 23 of the Fig. 1 embodiment. Centered between adjacent nozzles 45 are thin radial bafiles 46 which are attached to and in heat conducting relationship with the housing. Return lines 47 collect condensed vapor and return it to boiler 43. As in the diifusion pump,

35 the use of the improved nozzle and condensing surface in the ejector pump affords large entraining areas and consequently a high speed without undue backstreaming.

As stated previously, the drawing and description relate only to a preferred embodiment of the invention. Since many changes can be made in this embodiment without departing from the inventive concept, the following claims should provide the sole measure of the scope of the invention.

What is claimed is:

1. In a vapor pump of the type including a pumping vaporboiler, a jet chimney communicating with the boiler, a cooled casing spaced from and surrounding the chimney, a plurality of circumferentially spaced jet openings extending through the wall of the chimney, and inlet and outlet passages communicating with the space between the casing and the chimney at locations upstream and downstream, respectively, of said jet openings, the improvement which comprises a plurality of jet nozzles spaced around the periphery of the chimney, one being associated with each jet opening and each having an exit arranged to discharge pumping vapors in the direction of the outlet passage and a closed vapor transmitting passage connecting the jet opening with the exit; and a radial bafile located between each pair of adjacent nozzles, the battles being supported by and in heat-conducting relationship With the casing and defining confined spaces into which the nozzles discharge.

2. The improvement defined in claim 1 in which the cross-sectional area of each vapor transmitting passage 41- increases progressively from the jet opening to the nozzle exit and the passage is arranged to direct a portion of the vapors outward toward the casing.

3. In a vapor pump of the type including a pumping vapor boiler, a jet chimney communicating with the boiler, a cooled casing spaced from and surrounding the chimney, a plurality of circumferentially spaced jet openings extending through the Wall of the chimney, and inlet and outlet passages communicating with the space between the casing and the chimney at locations upstream and downstrem, respectively, of said jet openings, the improvement which comprises a plurality of jet nozzles spaced around the periphery of the chimney, one being associated with each jet opening and each having the shape of a projecting portion of a fluted thin-walled truncated cone, the nozzles projecting radially outward from the chimney and discharging in the direction of the outlet passage; and a radial bafile located between each pair of adjacent nozzles, the bafiies being supported by and in heat conducting relationship with the casing and extending, in the longitudinal direction, between points upstream and downstream of the nozzle exits.

47 The improvement defined in claim 3 in which the longitudinal faces of the radial bafiles are parallel with the outer periphery of the exit of the adjacent nozzle.

References Cited in the file of this patent FOREIGN PATENTS 1 ,128,516 France Ian. 7, 1957 

